The invention relates to a laser radiation source comprising an array of N individual slave laser diodes in a predetermined surface area, a slave power supply for the slave laser diodes, a master laser diode for generating a master laser radiation, a master power supply for the master laser diode, an optical coupling device, with which the master laser radiation can be coupled into the individual slave laser diodes in order to operate them at the frequency of the master laser diode in a phase-locked manner, and an optical transformation device which forms a coherent total laser radiation field with essentially defined, preferably plane wave fronts from the slave laser radiation of the individual slave laser diodes.
Laser radiation sources of this type are known from the state of the art.
In their case there is, however, the problem that the stable operation of the individual slave laser diodes is extremely complicated.
The object underlying the invention is, therefore, to improve a laser radiation source of the generic type in such a manner that the slave power supply has a separate power supply network for each slave laser diode, that each of the power supply networks can be adjusted with respect to the current supplied to the respective slave laser diode during a certain operating period for adjusting the slave laser diodes relative to one another and that the power supply networks are connected in parallel and supplied by a common source.
The advantage of the inventive solution is to be seen in the fact that it is possible, due to the adjustability of the power supply networks, for the slave laser diodes to be adjusted relative to one another and thus be operated in a stable manner in relation to one another.
At the same time, the relative stability of the operation of the individual slave laser diodes is improved further due to the fact that the power supply networks are connected in parallel and supplied by a common source since fluctuations in the supply by the common source affect all the slave laser diodes to the same degree and so the adjustment of the slave laser diodes relative to one another is not impaired.
Therefore, a possibility which is simple to realize is created by the inventive solution of adjusting an optionally large number of slave laser diodes relative to one another and of operating them in a stable manner in this adjustment relative to one another over a certain operating period.
Within the meaning of the inventive solution, it is, in this respect, possible to carry out the adjustment only for a certain operating period. For example, it would be conceivable to adjust the slave laser diodes relative to one another prior to putting them into operation each time by means of a procedure to be provided later in detail.
It is, however, even better when the slave laser diodes have to be readjusted relative to one another only at certain intervals, i.e. longer operating periods, so that the complicated adjustment of the slave laser diodes relative to one another can be omitted each time they are put into operation.
It is, however, particularly favorable when the slave laser diodes are adjusted relative to one another in that each of the power supply networks can be adjusted one time.
Such a one-time adjustability of a power supply network is known from circuit technology as a result of manifold solutions. For example, it is known to trim complex circuits one time so that these subsequently operate in accordance with the one-time trimming.
In principle, it is conceivable to construct the power supply networks in an optionally complex manner since complex circuit networks can also be produced in large numbers and in a simple manner with a modern design of electronic circuits. For example, it would be conceivable to design the power supply networks with adjustable current stabilizing circuits with the use of semiconductor components.
It is, however, particularly favorable when each of the power supply networks is a resistance network since a resistance network is, on the one hand, inexpensive to construct and, on the other hand, can be adjusted in a very simple manner.
A particularly favorable solution provides for each of the power supply networks to have a resistor adjustable due to alteration of its cross section.
In principle, it would also be conceivable to design the resistance network in such a manner that the adjustable resistor represents a parasitic current drain which is connected in parallel to the respective slave laser diode.
It is, however, particularly favorable with respect to the power consumption when each of the power supply networks has an adjustable resistor connected in series with the respective slave laser diode since, as a result, the current can be influenced in a direct manner by the slave laser diode and, in addition, the current consumption can be minimized.
The power supply networks could, in principle, be supplied by an optional common source. A particularly favorable solution provides for all the power supply networks to be supplied by a common voltage source so that the power supply networks can, in particular, be designed as simple resistance networks, with which the current can be determined in a simple manner by varying the resistance.
The common voltage source is preferably a voltage-stabilized voltage source so that fluctuations in the voltage can be avoided to a great extent and thus an additional stabilization of the adjustment of the slave laser diodes relative to one another can be achieved.
In principle, it would be conceivable to design the power supply of the master laser diode in accordance with the slave power supply and, for example, to likewise supply the slave power supply via the common source.
It is, however, particularly favorable with respect to the degrees of freedom of the adjustment of the master laser diode relative to the slave laser diodes when the slave power supply operates independently of the master power supply so that a completely independent operation of the master laser diode is possible.
In this respect, it is particularly expedient when the master power supply can be controlled with respect to the current through the master laser diode and thus a controlled modulation of the master laser radiation can, for example, be realized.
For example, it would also be possible by way of a controlled modulation of the master laser diode to modulate the intensity of the total laser radiation field, namely when the modulation of the master laser diode is carried out to such an extent that this no longer operates the slave laser diodes in a coupled manner.
As a result, it is possible, for example, in a simple manner and with a slight variation in the current to obtain a large modulation depth in the intensity of the total laser radiation field and thus to connect a large optical power even with a small current, wherein a quick connection of the large optical power is possible on account of the short response times in the interaction between the master laser radiation and the slave laser diodes.
In order to be able to design the operation of the slave laser diodes relative to one another to be as stable as possible it is preferably provided for all the slave laser diodes to be arranged on a common support.
It is particularly favorable for the production of the slave laser diodes when the common support for the slave laser diodes is a substrate, on which the slave laser diodes are installed during their production.
In principle, it would be conceivable to contact each individual slave laser diode with an electrical line for the power supply, similar to the procedure known from semiconductor technology of bonding semiconductors. It is, however, particularly favorable for realizing the power supply to the slave laser diodes when the power supply of the slave laser diodes is brought about by way of path conductors extending on the support.
For example, it would be conceivable in this respect, in the case of a two-dimensional array of slave laser diodes on one side of the substrate, to connect the slave laser diodes of one row to a common path conductor and on the opposite side of the substrate to connect rows of slave laser diodes extending transversely thereto to a common path conductor extending transversely to the first path conductor so that a so-called matrix activation of the slave laser diodes would be possible.
It is, however, particularly simple when all the slave laser diodes of an array on one side are connected to a common path conductor and on the opposite side are supplied by the respective power supply network.
In this respect, it is preferably provided for reasons of as simple a producibility as possible for the power supply networks for the slave laser diodes to be arranged on the support.
For example, it could be provided for the power supply networks to be positioned next to the array of slave laser diodes and for each of the power supply networks to be connected to the corresponding slave laser diode by a suitable path conductor.
It is, however, even more advantageous when a power supply network arranged on the support in the area of the respective slave laser diode is associated with each slave laser diode so that, for example, the power supply network is arranged in the immediate vicinity of the respective slave laser diode and thus all the power supply networks can, on the other hand, be supplied via the common source by way of common path conductors connecting all the power supply networks to one another.
In this respect, it is particularly favorable when the power supply network has conductor sections which are arranged on the support and can be adjusted with respect to their resistance since these can be arranged in a space-saving manner so that it is possible to provide the respective power supply network in the area of the respective slave laser diode and, on the other hand, can be adjusted in a simple manner.
In this respect it would, for example, be conceivable to provide a material variation for the adjustment. It is, however, particularly favorable when the conductor sections can be adjusted by way of variation of a cross section thereof, wherein a removal of material is also conceivable, for example, for the cross-sectional variation.
A variation in the cross section of a conductor section for the adjustment of the resistance is to be understood not only as a reduction in the cross section but also an increase in the cross section as well as the connection of two sections of a path conductor which are, first of all, interrupted for the purpose of decreasing the resistance.
A particularly favorable technology provides for each of the power supply networks to be adjustable by way of laser trimming since, as a result, an adjustment of the individual power supply networks relative to one another is possible in a particularly simple and inexpensive manner.
With respect to the adjustment of the slave laser diodes relative to one another, no further details have so far been given. One decisive criterion is the possibility of adjusting the slave laser diodes such that the slave laser radiations are superimposed coherently to form the total laser radiation field.
In this respect it is particularly favorable when each slave laser diode is designed such that a resonator frequency of the slave laser diode can be adjusted by adjusting the current in order to set the operating range of the slave laser diode such that this operates at the frequency of the master laser radiation.
In addition, a critical parameter for the adjustment of the slave laser diodes relative to one another is the phase relationship of the slave laser radiation.
For this reason, it is particularly favorable when a phase relationship of the slave laser radiation of each slave laser diode relative to the phase of the master laser radiation can be adjusted by adjusting the current.
With this solution there is the great advantage that the slave laser diodes will not only be operated relative to one another at the same frequency and in a phase-locked manner due to the master laser diode but there is also the possibility of adjusting the individual slave laser diodes in their phase relationship to the master laser radiation, in addition to the phase-locked operation, and thus, for example, of compensating for phase differences caused by different optical wavelengths so that the slave laser radiations are actually superimposed in phase to form the coherent total laser radiation field.
With respect to the arrangement of the individual slave laser diodes, no further details have so far been given. It would, for example, be conceivable to arrange the slave laser diodes as desired, also, for example, in a row.
It is, however, particularly advantageous when the slave laser diodes are arranged in a two-dimensional array.
Such a two-dimensional array could still be an irregular pattern. It is, however, particularly favorable when the slave laser diodes are arranged in the two-dimensional array in a regular pastern in order to be able, in particular, to also design and adjust the optical transformation device accordingly.
Such a two-dimensional array could be designed in such a manner that it still has an elongated shaped.
In order to be able to utilize the optical components particularly advantageously and, in particular, to obtain as favorable a spatial distribution of intensity as possible in the coherent total laser radiation field, it is preferably provided for the two-dimensional array to have an extension of approximately the same order of magnitude in each dimension.
The two-dimensional array is preferably such that it has essentially the same order of magnitude in each dimension.
With respect to the arrangement of the slave laser diodes and the master laser diode relative to one another, no further details have been given in conjunction with the preceding explanations concerning the individual embodiments of the invention. It would, for example, be conceivable to provide the master laser diode completely separately from the slave laser diodes since, theoretically, the optical coupling of the master laser diode to the slave laser diodes is sufficient.
However, in order to be able to operate the master laser diode in a similar manner to the slave laser diodes with respect to the environmental conditions, in particular, the temperature conditions and also in order to be able to produce the master laser diode in as similar a manner as possible to the slave laser diodes with respect to its overall specifications it is preferably provided for the slave laser diodes and the master laser diode to be seated on the same support. It is even more advantageous when the slave laser diodes and the master laser diode are seated on the same substrate.
A particularly favorable laser diode provides for one of the laser diodes of a continuous array of laser diodes to represent the master laser diode and the other laser diodes to operate as slave laser diodes. This means that first of all an array of laser diodes is produced which are as identical as possible, one of the laser diodes is selected as master laser diode and the remaining laser diodes are then operated as slave laser diodes.
With respect to the design of the laser diodes themselves, no specific details have been given in conjunction with the preceding explanations concerning the inventive solution. It would, in principle, be conceivable to use so-called edge emitters as laser diodes.
However, since such edge emitters may preferably be inexpensively produced only together as one-dimensional arrangements and therefore two-dimensional arrangements of edge emitters would entail a more complicated production procedure, it is preferably provided for the laser diodes to be arranged on a single, continuous substrate as vertical emitters.
Vertical emitters of this type, or also called VCSELs, may be constructed in a particularly simple manner on a common substrate by way of known production processes, wherein the structure is produced, for example, by way of implantation, by way of mesa etching or by way of mesa etching and oxidation of the current diaphragm.
Furthermore, such vertical emitters have the advantage that they may be contacted in a simple manner since a common contacting of all the vertical emitters may be brought about via the substrate and, as for the rest, each individual vertical emitter may likewise be contacted selectively on its outlet side for the laser radiation in a simple manner.
Such a two-dimensional arrangement of vertical emitters thus creates the possibility of providing path conductors for the power supply in the areas between the vertical emitters and the corresponding power supply network, for example, in the form of adjustable resistors associated with each respective vertical emitter.
No details have been given in conjunction with the preceding explanations concerning the individual embodiments as to how the optical transformation device is intended to be designed.
The optical transformation device can, in principle, be of any optional design as long as the total laser radiation field can be formed with it from the slave laser radiations.
It is conceivable, for example, for the optical transformation device to comprise a microlens array. In this respect, it is preferably sufficient in the simplest case when the optical transformation device exclusively comprises a microlens array.
The optical transformation device can, however, be designed, in addition, as a complex optical device, into which a microlens array can, for example, likewise be integrated.
One advantageous solution of an optical transformation device provides for this to have a phase plate which alters the phase of the slave laser radiation in such a manner that a defined distribution of intensity results in an additional plane and for the optical transformation device to comprise in the additional plane a phase corrector plate which is adjusted to the first phase plate and leads to a defined wave front in the exiting total laser radiation field.
A defined wave front of this type can, in principle, have the most varied of shapes; it is particularly advantageous when the defined wave front is an essentially plane wave front.
A particularly expedient solution provides for the optical transformation device to have a phase plate which gives each slave laser radiation of a slave laser diode a different phase and for the optical transformation device to comprise a Fourier optical device, in the Fourier plane of which a phase corrector plate is arranged which is adjusted to the first phase plate and again conveys the same phase to the slave laser radiations having different phases and thus leads to the defined, plane wave front in the exiting total laser radiation field.
With such an optical transformation device, an essentially uniform, spatial distribution of intensity may, on the one hand, be created in the total laser radiation field with plane wave fronts, wherein the essentially uniform distribution of intensity can, for example, be a distribution of intensity similar to a Gaussian profile or a so-called flat top profile.
In principle, the phase plate can be designed such that it conveys to the various slave laser radiations a statistical phase shift relative to one another.
It is, however, particularly favorable for achieving as high an intensity as possible at as uniform a spatial distribution of intensity as possible when the phase plate effects a phase shift determined by an algorithm between the slave laser radiations of different slave laser diodes.
One particularly advantageous algorithm provides for the phase plate to effect a phase relationship varying in the same manner in all directions proceeding from a center point.
A particularly favorable embodiment provides for the variation in the phase relationship in all directions to be brought about in accordance with a monotonic analytical function.
No further details have so far been given with respect to the relationship between the optical coupling device and the optical transformation device. It would, for example, be conceivable to design the optical coupling device completely independently of the optical transformation device and thus configure the coupling completely independently of the optical transformation device.
One particularly favorable solution provides for the optical coupling device to couple the master laser radiation into the slave laser diodes via the optical transformation device. As a result, the possibility is created of coupling the master laser radiation into the individual slave laser diodes in a simple and efficient manner.
In this respect, it is preferably provided for the master laser radiation to pass through not only the phase corrector plate but also the phase plate.
With respect to realizing the optical transformation device, it would, in principle, be conceivable to construct this in a known manner in individual optical components, for example, lenses and phase plates.
A particularly favorable solution for a commercial realization provides for the optical transformation device to be integrated in a coherent block since such a coherent block is, in particular, insensitive to adjustment and can also be produced in large numbers in a simple manner.
In this respect, it is preferably provided for the elements of the optical transformation device to be designed as elements of diffractive optics, i.e. not only the lenses but also the phase plates are elements of diffractive optics which may be realized in the respective surfaces of the coherent block, for example, by way of etching methods.
In this respect, it is particularly favorable when the optical coupling device is also integrated into the coherent block.
In addition, the object specified at the outset is accomplished in accordance with the invention, in a process for operating a laser radiation source comprising an array of N individual slave laser diodes, a master laser diode for generating a master laser radiation, an optical coupling device, with which the master laser radiation is coupled into the individual slave laser diodes in order to operate them at the frequency of the master laser diode in a phase-locked manner, and an optical transformation device, with which a coherent total laser radiation field with essentially defined wave fronts is formed from the slave laser radiation of the individual slave laser diodes, in that the current supplied to each individual slave laser diode during a certain operating period is adjusted individually for adjusting the slave laser diodes relative to one another such that the slave laser radiations are superimposed coherently in the total laser radiation field with the same phase.
The advantage of the inventive process is to be seen in the fact that with it a simple possibility of adjusting the slave laser diodes relative to one another is made available for the first time in order to be able to superimpose the slave laser radiations in the total laser radiation field coherently since only an adjustment of the current supplied to each individual slave laser diode is sufficient to bring about the coherent superposition of the slave laser radiations to form the total laser radiation field.
The term xe2x80x9cadjustmentxe2x80x9d is to be understood in this respect as an adjustment for operating periods to be respectively determined. Operating period is to be understood, for example, as the duration of the respective operation of the slave laser diodes from a one-time switching on until a switching off. However, an operating period is also to be understood as a longer operating period, for example, of days, months or years, for which a one-time adjustment is sufficient.
It is particularly advantageous when the current for each individual slave laser diode is adjusted one time so that all the slave laser diodes are adjusted relative to one another during their entire service life as a result of a one-time adjustment.
In principle, it would be conceivable within the scope of the inventive solution to operate the master laser diode coupled to the slave laser diodes, i.e. also adjusted relative to them. It is, however, particularly favorable when the slave laser diodes are operated independently of the master laser diode since it is then possible to adjust the master laser diode to the slave laser diodes in an optimum manner.
A particularly favorable solution provides for the total laser radiation field to be modulatable with the master laser diode.
In this respect, it would be conceivable, on the one hand, to modulate the master laser radiation optically, for example, as a result of beam interruption or beam attenuation or rotation of polarization. It is, however, particularly favorable when the master laser radiation can be modulated by way of the current supplied to the master laser diode since, as a result, such a modulation of the master laser radiation which effects a decoupling of the slave laser diodes from the master laser diode is possible due to a small current alteration and so the slave laser diodes no longer operate in a frequency-locked and phase-locked manner and therefore the coherent superposition of the slave laser radiations to form the total laser radiation field breaks down and so, in the long run, a small current modulation leads to an essentially complete modulation of the intensity of the total laser radiation field.
With respect to the operation of the individual slave laser diodes, no specific details have been given in conjunction with the preceding explanations concerning the individual embodiments. It is particularly advantageous, in order to maintain the adjustment of the slave laser diodes relative to one another, when all the slave laser diodes are operated under identical temperature conditions, for example, are arranged on a common support or substrate and attemperated by this.
It is also particularly favorable when the slave laser diodes and the master laser diode are operated under essentially identical temperature conditions so that drifts of the master laser diode relative to the slave laser diodes triggered by temperature are also avoided.
With respect to the design of the slave laser diodes, it has proven to be particularly favorable when each of the slave laser diodes is designed with respect to its operating range as a slave laser diode such that a resonance frequency of the slave laser diode is adjusted by way of adjustment of the current. As a result, it is possible due to the adjustment of the current to alter the resonance frequency of the respective slave laser diode and thus adjust this with respect to the frequency of the master laser radiation, as well.
It is particularly advantageous when a phase relationship of the slave laser radiation of each slave laser diode relative to the master laser radiation is adjusted by way of adjustment of the current since, as a result, it is possible to adjust the phase of the respective slave laser diode individually such that in the total laser radiation field the slave laser radiations of all the slave laser diodes can be superimposed in phase.